Low voltage indicator circuit



Sept. 26, 1967 Y J. L. ATKINSON 3 3 8 LOW VOLTAGE INDICATOR CIRCUIT Filed Maz ch 10, 1965 III: m p-J. N 20 mm FIG. 2(0) INVENTOR. JAMES L. ATKINSON ATTORNE United States Patent 3,344,308 LOW VOLTAGE INDICATOR CIRCUIT James L. Atkinson, La Mirada, Califl, assignor to North American Aviation, Inc. Filed Mar. 10, 1965, Ser. No. 438,620 2 Claims. (Cl. 315-135) ABSTRACT OF THE DISCLOSURE A transistor circuit for operating a neon lamp in which a transistor effectively shorts a portion of a voltage divider load having a parallel branch containing the neon lamp placing the full supply voltage across the lamp. When the transistor is in the non-conductive state the voltage across the lamp is substantially lower than that required to fire the lamp. A unidirectional pulsating potential is used to decrease the voltage change required across the transistor for switching the lamp on and off.

This invention relates in general to an indicator circuit and in particular to a transistor circuit for indicating elec trical conditions in circuits characterized by relatively low voltage differentials.

In electronic systems, particularly computer systems, it is necessary to provide means for visually indicating the state of various electronic circuits contained within the system. Glow discharge lamps, such as neon lamps, have found extensive use for just such purposes.

Circuits presently used to operate such lamps may re quire a knowledge of the neon lamps ignition voltage and its extinction voltage and the range of these voltages for randomly selected lamps. Other circuits require the use of two or more power supplies. Also to be considered are the required number of components, along with the high cost of certain types of components such as diodes, capacitors and inductors. In systems requiring a multitude of indicators, a decisive cost savings may be obtained with an indicator which does not require these components.

It is accordingly an object of this invention to provide a new and improved indicator utilizing glow discharge lamps.

Another object of this invention is to provide an indicator circuit for reliably firing and extinguishing glow discharge lamps with a minimum of power.

A further object of this invention is the provision of an indicator circuit which operates substantially independent of the characteristics of glow discharge lamps.

A still further object of this invention is to provide a low cost indicator circuit utilizing glow discharge lamps.

Another object of this invention is to provide an indicator circuit utilizing a low voltage transistor.

In accordance with the present invention a single transistor, when in the conductive state, effectively shorts across a portion of a voltage divider load having a parallel branch containing the glow discharge lamp, placing the full supply voltage across the lamp. When the transistor is in the nonconductive state, the voltage across the lamp is substantially lower than that required to fire the lamp.

These and other objects and advantages of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of the preferred embodiment of the invention; and

FIGS. 2(a) and 2(b) illustrate voltage waveforms for use in the embodiment of FIG. 1.

Referring to FIG. 1,- there is shown a PNP transistor 11 having an emitter electrode 11e, a base electrode 11b 3,344,308 Patented Sept. 26, 1967 and a collector electrode 11c. Collector electrode 11c is connected through a 62K ohm load resistor 17 to a potential source e at terminal 16.

Collector electrode 110 is also connected by a 30K ohm resistor 20 to emitter electrode 11e of transistor 11, which in turn is connected to a common terminal (ground). The unidirectional pulsating potential supply e having a value of 90 volts is connected across terminal 16 and the common terminal (ground).

Resistors 17 and 20 form a voltage divider which places approximately 30 volts maximum 0n collector 110 of transistor 11 when transistor 11 is in the OFF or nonconducting state. A 100K resistor 18 is serially connected to a glow discharge lamp 19 which may be a neon lamp such as an NE75. The series combination of resistor 18 and lamp 19 is connected across (in parallel with) resistor 17.

Base 11b of transistor 11 is connected by a 24K resistor 15 to a bias terminal 14 having +3 volts DC applied thereto with respect to the common terminal. Also, connected to base 11b is a 10K resistor 13 which in turn is connected to an IN terminal 12.

In FIG. 2(a) the waveform for the unidirectional pulsating source e is shown. This waveform varies from 0 volts to 90 volts DC. This is a well known type of waveform generated in a full wave rectifier which has no filter at its output. Another waveform which may be used effectively is shown in FIG. 2(b). This waveform is a clipped 220-vo1t wave also obtained from a full wave rectifier without an output filter. The use of the waveform shown in FIG. 2(b) provides an improvement in the ON and OFF duty cycle of glow discharge lamp 19. The period which the lamp is ON is increased so as to give almost as bright an appearance as if the supply were DC.

In operation with transistor 11 OFF or nonconducting, the impedance from collector electrode 11c to emitter electrode 11a is quite high; hence, very little current flows through this path except for small leakage currents. Resistors 17 and 20 will then form a simple voltage divider for the voltage e with approximately 30 volts maximum across resistor 20 and volts maximum across resistor 17. In general, the V min. for NE-75 lamps is 65 volts; therefore, lamp 19 does not have enough voltage across it to fire because with a total supply voltage of 90 v., only a 60-volt differential will be felt across resistor 17 When approximately 3 volts is applied to IN terminal 12, transistor 11 is turned ON placing collector 110 at approximately the common terminal potential (ground). Substantially all current flow will now be through the collector-emitter electrodes of transistor 11. Resistor 20 is effectively shunted and the junction of resistors 17 and 20 placed at effective ground. The total potential e is now applied across resistor 17 and the series combination of resistor 18 and lamp 19. The magnitude of the voltage across the lamp will be volts, enough to cause the lamp to fire. Resistor 18 limits the amount of current drawn by lamp 19.

When the 3 volts is removed from the base of transistor 11, the transistor is turned OFF and the junction of resistors 17 and 20 again rises to a maximum of 30 volts. The potential e is periodically cycling from 0 volts to 90 volts; during this cycle the voltage across resistor 17 will drop in value well below the extinguishing potential of lamp 19 and the lamp will be turned off. From the previous description it is shown that the lamp is full-on when the transistor is ON (conducting) and is full-off when the transistor is OFF (nonconducting). This operation offers a decided savings in power.

While there has been shown and described a preferred embodiment of the invention, it will be understood that 3 various omissions, substitutions, and changes in the form and details of the circuit illustrated and in its operation may be made by those persons skilled in the art without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. An indicator circuit comprising in combination:

a glow discharge lamp having a firing potential and an extinguishing potential;

a source of unidirectional periodic pulsating potential whose peak amplitude is greater than said firing potential, said source having first and second terminals;

a first and a second resistor serially connected between said first and said second terminals to form a potential divider with the potential across said first resistor being below said firing potential;

a third resistor connected in series with said glow discharge lamp across said first resistor;

a transistor having base, emitter and collector electrodes, said collector-emitter electrodes connected across said second resistor;

2,927,247 3,225,215 12/1965 Winter 315-135X an input terminal responsively connected to said base for receiving input pulses for turning said transistor ON and OFF such that in said ON condition substantially all current flow through said second resistor is bypassed and the potential across said first resistor is periodically above said firing potential and in said OFF condition the potential across said first resistor is never above said firing potential.

2. The indicator circuit of claim 1 wherein said uni- 0 directional periodic pulsating potential is a clipped full wave rectified sinusoidal signal so as to increase the time during which said potential is above said firing potential.

References Cited UNITED STATES PATENTS 3/1960 Hennis 315-135 20 JAMES W. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner. 

1. AN INDICATOR CIRCUIT COMPRISING IN COMBINATION: A GLOW DISCHARGE LAMP HAVING A FIRING POTENTIAL AND AN EXTINGUISHING POTENTIAL; A SOURCE OF UNIDIRECTIONAL PERIODIC PULSATING POTENTIAL WHOSE PEAK AMPLITUDE IS GREATER THAN SAID FIRING POTENTIAL, SAID SOURCE HAVING FIRST AND SECOND TERMINALS; A FIRST AND SECOND RESISTOR SERIALLY CONNECTED BETWEEN SAID FIRST AND SAID SECOND TERMINALS TO FORM A POTENTIAL DIVIDER WITH THE POTENTIAL ACROSS SAID FIRST RESISTOR BEING BELOW SAID FIRING POTENTIAL; A THIRD RESISTOR CONNECTED IN SERIES WITH SAID GLOW DISCHARGE LAMP ACROSS SAID FIRST RESISTOR; A TRANSISTOR HAVING BASE, EMITTER AND COLLECTOR ELECTRODES, SAID COLLECTOR-EMITTER ELECTRODES CONNECTED ACROSS SAID SECOND RESISTOR; AN INPUT TERMINAL RESPONSIVELY CONNECTED TO SAID BASE FOR RECEIVING INPUT PULSES FOR TURNING SAID TRANSISTOR ON AND OFF SUCH THAT IN SAID ON CONDITION SUBSTANTIALLY ALL CURRENT FLOW THROUGH SAID SECOND RESISTOR IS BYPASSED AND THE POTENTIAL ACROSS SAID FIRST RESITOR IS PERIODICALLY ABOVE SAID FIRING POTENTIAL AND IN SAID OFF CONDITION THE POTENTIAL ACROSS SAID FIRST RESISTOR IS NEVER ABOVE SAID FIRING POTENTIAL. 